Copper(II) Ions Convert Catechins from Antioxidants to Prooxidants in Protein Carbonyl Formation

Abstract

Catechins are naturally occurring polyphenols, which are supposed to have antioxidative effects on foods and living cells. We examined the antioxidative effects of (+)-catechin and 3-O-acyl derivatives of (+)-catechin in combination with copper(II) [Cu(II)] ions on the formation of carbonyl groups in bovine serum albumin (BSA) at pH 7.4 by incubating in vitro for 90 min at 37°C. In the presence of 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), a free radical generator, the formation of carbonyl groups in BSA, which increased time-dependently, was significantly (p<0.05) attenuated by the addition of (+)-catechin and 3-O-acyl-(+)-catechins. However, Cu(II) ions, but not Zn(II) ions, blocked the antioxidative effects of (+)-catechin and 3-O-octanoyl-(+)-catechin on the oxidative modification of BSA induced by AAPH. On the other hand, Cu(II) ions had no influence on the scavenging activity of (+)-catechin for 2,2'-azinobis(3-ethylbenzothiazoline-6-sulphonate) cation radicals. Furthermore, in the absence of AAPH, coexistence of Cu(II) ions with (+)-catechin greatly accelerated the formation of carbonyl groups in BSA, being dependent on the concentrations of Cu(II) ions and (+)-catechin. These results suggest that Cu(II) ions could convert (+)-catechin from an antioxidant to a prooxidant in protein oxidation.